Drill string stabilizer



Dec. 31, 1968 R. A. 8080 3,419,094

DRILL STRING STABILIZER Filed June 17, 1966 Sheet of z y ,4. 5am INVENTOR d; f M:

MM W 1 ATTORNE Y Dec. 31, 1968 R. A. 8050 DRILL STRING STABILIZER Sheet 2 Filed June 17, 1966 Roy A. .5050 LVVEJVTQR BY 7 8 M.

3,419,094 DRILL STRING STABILIZER Roy A. Bobo, Houston, Tex., assignor to Reed Roller Bit Company, Houston, Tex.. a corporation of Texas Fiied June 17, 1966, Ser. No. 558,344 1 Claim. (Ct. 175325) ABSTRACT OF THE DISCLOSURE A stabilizer or guide for a deep well drilling string on which there are provided means near the bit to control the rate of change of hole direction angle or of holding such rate of deviation from the vertical to a minimum during drilling and avoid spiralling of the bore hole. The stabilizer or stabilizers are constructed so that the ratios or areas of the return passageways with respect tothe size of the stabilizer are in some predetermined relation to the size of the stabilizer and the flutes or the passageways have depths such that a good hydraulic radius is maintained and maximum stiffness of the stabilizer is afforded.

Brief summary the invention The stabilizer of the invention has a diameter substantially equal to the nominal hole diameter with very small diametrical differences between the diameter of the stabilizer and the diameter of the bore hole. The placing of one stabilizer adjacent the bit and the spacing of other stabilizers at points less than the normal buckling height of the drill string components result in a packed hole assembly which is very stiff and tends to minimize the tendency of the bit to deviate from a vertical path. A suitable arrangement of the stabilizers is in the placing of one immediately above the drilling bit, another approximately 12 feet thereabove and a third stabilizer approximately 36 feet about the second stabilizer, thus placing the assembly so that the upper stabilizer is approximately 48 feet from the bit; the middle stabilizer is approximately one-fourth the distance from the bit to the top stabilizer, the bottom stabilizer being placed immediately above the bit. The stabilizer of the invention materially benefits rock bit performance because a more uniform loading of the bit is achieved.

This invention relates generally to rotary well drilling apparatus and more particularly to a stabilizer or guide for a deep well drilling string.

It is an object of this invention to provide a new and improved stabilizer which is effective to stabilize a rotaryrock bit by providing means near the bit to control the rate of change of hole direction angle or of holding such rate of deviation from the vertical to a minimum during the drilling operation.

Another object of this invention is to provide a new and improved stabilizer which guides and stabilizes the drill string in the hole and yet provides for the free passage of drilling fluid thereby.

Another object of the invention is to provide a new and improved stabilizer which will minimize spiralling of the bore hole.

Another object is to provide a stabilizer by which the drill string may be maintained in a centered position in the well bore to aid in the drilling of a straight, as well as a vertical, bore hole.

Another object of the invention is to provide a stabilizer designed to alleviate lateral deflection of the bit caused by obstructions such as hard irregular and slanting geological formations thereby overcoming difl iculties which may result from a crooked hole which may prevent insertion of casing and may cause the drill string to stick in the bore hole.

Another object is to provide a drill string stabilizer that is simple in construction, inexpensive to manufacture, eflicient in operation and capable of withstanding extreme conditions of wear and hard usage to which such equipment is customarily subjected.

Another object is to provide a drill string stabilizer having a new and improved configuration of lands and flutes to enhance the bearing capacity of the stabilizer and to permit free passage of drilling fluid thereby.

Another object is to provide a drill string stabilizer having a new and improved arrangement of hard metal on the lands thereof.

Another object is to provide a new and improved stabilizer which is extremely rigid whereby more useful weight may be applied to the drilling bit and whereby such weight is more evenly or uniformly distributed.

Another object is to provide a drill string stabilizer having an eflicient hydraulic radius for the return fluid passageways whereby the hydraulic radius and the area of the return passageways will stay within acceptable limits for fluid flowing therethrough.

Another object is to provide fluid passageways in a drill string stabilizer wherein the ratios or areas of the return passageways with respect to the size of the stabilizer are in some predetermined relation to the size of the stabilizer.

Another object is to provide a stabilizer wherein the depths of the flutes or the passageways is such that a good hydraulic radius is maintained and maximum stiffness of the stabilizer is afforded.

Another object is to provide a drill string stabilizer wherein the Width of the flutes or passageways has a predetermined relation to the size and dimension of the stabilizer and to the axial bore therethrough.

Another object is to provide a stabilizer wherein the the diameter of the stabilizer is substantially the same as the nominal diameter of the hole being drilled.

Another object is to provide an arrangement of drill string stabilizers to control the rate of change of hole angle and to hold the rate of deviation from the vertical to a minimum.

Another object is to provide a stabilizer having a lateral bearing surface above and as close to the drilling bit as is practicable.

Another object is to provide a stabilizer to hold the drilling bit in the center of the hole as drilling progresses and thereby prevent spiralling, abrupt doglegs and ledges and the like of the hole being drilled.

A still further object is to provide a stabilizer arrangement to afford support against buckling of the drill string when such stabilizers are used at a suitable point or points above the drilling bit.

Another object of the invention is to provide a new and improved hard metal arrangement on the stabilizer lands whereby a portion of the drilling fluid may be circulated between ridges of hard metal to cool and lubricate the same and to alleviate wear of the stabilizer lands.

In the rotary drilling of deep wells, the formations penetrated by the drill bit are frequently composed of alternate hard and soft streaks, which may be disposed or bedded in planes at angles other than normal to the direction of drilling. This condition, coupled with the tendency of the drill string to buckle under compressive loads, may result in deviation of the bore hole from a desired path. The stabilizer of the invention effects a stiffening and centering of the lower portion of the drilling string, and immediately adjacent the drill bit to alleviate the tendency of the bit to deviate from the established center of the hole previously drilled.

This invention also consists in certain other features of construction and the combination or arrangement of the several parts as are fully described herein, and as will be best understood from the following description and the accompanying drawings, in which:

FIGURE 1 is a vertical view of a portion of a drill string, showing the new and improved stabilizer.

FIGURE 2 is an enlarged view of one of the stabilizers shown in FIGURE 1.

FIGURE 3 is a schematic view, showing an arrangement of stabilizers in a drilling string,

FIGURE 4 is a schematic view, showing in exaggerated fashion, a spiralled bore hole.

FIGURE 5 is a cross-sectional view taken along line 55 in FIGURE 2.

FIGURE 6 is an enlarged detail view, showing a different configuration of the stabilizer land and passageway.

FIGURE 7 is an enlarged detail view similar to FIG- URE 6, showing another configuration of the stabilizer land and passageway.

Referring to FIGURE 1, the bore hole is shown generally at 10 and a drill String is shown generally at 11. A drilling bit is shown schematically at 12 and a lower stabilizer 13 is shown immediately above: the drilling bit 12. A drill collar 14, which may be on the order of 30 feet long, is threadedly connected to the upper portion of the stabilizer 13. An upper stabilizer 15 is connected to the upper end of the drill collar 14. The upper end of the stabilizer 15 is connected into the drill string which extends from the surface of the earth and is rotated by the rotary table.

The drill string is usually comprised of hollow tubular sections which are arranged to be threadedly connected end to end to each other and to stabilizers and drill collars which have axial bores therethrough. The drilling bit is connected to the lower end of the lowermost member and is arranged to have drilling fluid circulated therethrough.

The drill bit which is connected to the lower end of the drill string is rotated to cause the drill bit cutters to roll on the formation to thereby cut or crush the same. A mud laden drilling fluid is pumped downwardly through the drill string and bit and rises upwardly in the space between the drill string and the Wall of the bore hole to the surface of the earth. It is usually desired that the hole being drilled remain as nearly vertical as possible so that the well may be bottomed with some degree of accuracy, and it is also desired that the hole not have spirals, abrupt doglegs or ledges so that casing or other tools may be inserted into the bore without any danger of sticking the same.

It has been found that a drilling bit drills a hole slightly larger than its nominal diameter so that it is possible to make the stabilizer of the invention having a diameter substantially equal to the nominal hole diameter with very small diametrical differences between the diameter of the stabilizer and the diameter of the bore hole. The placing of one stabilizer adjacent the bit and the spacing of other stabilizers at points less than the normal buckling height of the drill string components result in a very effective packed hole assembly which is very stiff and which tends to minimize the tendency of the bit to deviate from a vertical path.

Since it is impossible to maintain zero diametrical differences between the stabilizers and the wall of the bore hole, the assembly may bend at least slightly when sufflcient lateral forces are applied, thus the stabilizers are located to minimize such bending.

Referring to FIGURE 3, we have found that a suitable arrangement of the stabilizers is in the placing of stabilizer 13 immediately above the drilling bit 12 and a stabilizer 15 approximately 12 feet above the stabilizer 13 and another stabilizer 16 approximately 36 feet above the stabilizer 15; thus this assembly places the upper stabilizer approximately 48 feet from the bit, and the middle stabilizer is approximately one-fourth the distance from the bit to the top stabilizer. The bottom stabilizer is placed immediately above the bit. The arrangement just described has been found to be effective in most formations.

It has been found that the round fluted configuration offers the best stabilizing and wear characteristics for the stabilizer while retaining several distinct advantages. The round stabilizers are substantially stifler than square sections, for example, and the round configuration has approximately three times as much bearing area, thus reducing the wall penetration of the stabilizers and adding materially to the effectiveness of the wall support.

As can be seen in FIGURE 5, the stabilizer '13 has an axial bore 17 therethrough. It has three flutes or passageways 18 extending longitudinally of the stabilizer. The lands 19 have hard metal 20 'which may he tungsten carbide or the like applied to the body of the stabilizer 13, which is usually made of an alloy steel such as A181 4137 or the like. The tungsten carbide 20 is shown here arranged on the lands 19 in ribs so as to provide grooves or auxiliary passageways 21 extending longitudinally of the stabilizer 13. These passageways 21 provide for some flow of the drilling fluid therethrough in order to alleviate wear and to cool and lubricate the bearing surfaces of the stabilizer during drilling operation. The hard metal 20 may be applied to the stabilizer 13 in any suitable manner and it is contemplated that the hard metal may comprise a sintered tungsten carbide in a special nickel-steel matrix to enhance wear characteristics.

As shown in FIGURE 2, the stabilizer 13 has a reduced cylindrical portion 22 at its upper end to provide space for tongs so that the member may be screwed into or unscrewed from the other drill string components.

As can be seen in FIGURE 4, an exaggerated spiralling condition of the hole is shown. Such spiralling condition may exist when the string is not properly stabilized and while the hole may have a nominal diameter as shown at letter A, the effective diameter may be closer to that shown at B, which is a projection of the clear passageway available for the insertion of casing or the like. Thus, it can be seen, that the prevention of such spiralling is highly desirable, and it has been found that the stabilizer of the invention tends to alleviate such spiralling.

While the round configuration for the stabilizer has many advantages, such as increased bearing surface available to bear against the wall of the bore hole, it is also important that sufficient area for the return of the drilling fluid be provided without substantially reducing the stiffness of the stabilizer. I prefer to use three return flutes or passageways 18, which have an efiicient hydraulic radius. In other words, the cross-sectional area relationship of each of the passageways 18, through which fluid is flowing, to the wetted perimeter of such passageway is such which will closely approach that of a circle of a square within the practical limits of the stabilizer. It will be noted that the distance between the point C and point D is substantially the same dimension as the diameter of the bore 17. I also have found that the depth of the flute or passageway is extremely efficient if it is between .140 and .221 times the diameter of the lower enlarged portion of the stabilizer 13. It is to be noted that the sides of the flute 18 lie in radial planes, and as passageway optimums, the sides of the flute 18 may lie in such radial planes as shown, but may be widened to lie in planes extending from point C and D, to be tangent to the diameter of the bore 17. In other words, it is preferred that the flute cross-sectional area be effected by obtaining the largest practical hydraulic radius. The combination of area and hydraulic radius will depend upon the acceptable pressure loss through these flutes or passageways. Further consideration is that the rising velocity of return fluid should be limited to a safe value where it will not appreciably erode either the steel of the stabilizer or the formation during its upward travel through the flutes. While the flutes here have been shown as extending longitudinally along the stabilizer in a straight line, it will of course be apparent that such flutes may be spiralled along the stabilizer if so desired.

Referring to FIGURE 6, another embodiment of the invention is shown wherein the stabilizer 13 has hard metal ribs 20 and may have a portion of a hard metal rib 23, bevelled or rounded as shown at 24 to lessen the likelihood of this leading edge digging into the formation and scraping off filter cake from the wall of the bore hole. This embodiment will also facilitate passage of drilling fluid between the bearing surface and the wall of the hole, enhancing the lubrication thereof and adding to the bearing effect of the stabilizer.

Similarly, referring to FIGURE 7, a portion of a stabilizer 13a is shown having hard metal ribs 20 and having a modified flute 18a wherein the leading or trailing portinos, or both, of the flute 18a may have added thereto shoes or padded areas 2 5 to add to the bearing area of the stabilizer and to reduce the area of the flute which is exposed to the wall of the bore hole and thus subjected to the eroding effect of'return fluid. This configuration does not appreciably affect the passage-way area or hydraulic radius and such configuration adds to the overall stiffness of the stabilizer.

The grooves or auxiliary passageways 19 between the hard metal ribs 20 serve to provide fluid lubrication for the stabilizer bearing surface against the wall of the bore hole as the stabilizer rotates therein, and serve to sweep away any free abrasive particles which may have escaped from the main fluid return passageways. They also serve to provide cooling for the bearing surfaces, and together with the return flutes 18, alleviate differential pressure sticking of the drill string in the bore hole.

Referring again to FIGURE 5, the width of the passage- Way '18 as denoted by the distance CD on the outer periphery of the stabilizer is controlled by the central angle G that is subtended by radii drawn from the respective points C and D to the center of the stabilizer O. I have found from practical considerations and from. calculations that this central angle preferably should be not less than 30 degrees and not more than 45 degrees.

The sides of the passageway 18 may be within a range bounded by the radii of central angle G to sides that are parallel to a line OE drawn from the center of the stabilizer through a mid-point F between points C and D.

As as been stated, the stabilizer of the invention maten'ally benefits rock bit performance because a more uniform loading of the bit is achieved. Field observations reveal that bits run with the stabilizer of the invention have fewer broken teeth and the bearing wear thereof is more evenly distn'btued among the cutters. Further, use of the stabilizer actually eliminates undersize holes and results in faster, more trouble free and more economical well drilling, particularly when running in known crooked hole areas.

In operation, as the drilling bit and drill string progress downwardly through the formation being drilled, the drilling bit fractures the formation causing lateral forces which tend to deflect the bit. As drilling progresses, if these lateral forces are not restrained, the hole angle will increase. As more weight is applied to the bit, the formation fractures in larger portions, creating greater lateral forces and causing a more rapid deviation of the drilling string from the desired direction. The stabilizer of the invention tends to hold the bit in its original path while the fractured formation is drilled away. When the stabilizer anrangementof the invention is run in a vertical or nearly vertical hole it acts to keep the hole vertical. As shown in the arrangement of FIGURE 3, the top stabilizer will resist the lateral forces caused by buckle of the upper string; the middle stabilizer will resist the lateral forces caused by the bending between the top and middle stabilizer and the lower stabilizer being near the bit resists lateral forces on the hit. As formations are encountered which tend to cause the deviation angle to increase, the arrangement resists this tendency.

This invention has been described herein in connection 'with specific embodiments of the same, but it will be understood that these are intended by way of illustration only and that numerous changes can be made in the construction and arrangement of the various parts without departing from the spirit of the invention or the scope of the appended claim.

What is claimed is:

1. A stabilizer for use in a well bore drilling string having a bit at the lower end thereof and adapted for placement on said string immediately above said bit, a second like stabilizer in said drill string remote from said drilling bit, a third like stabilizer in said drill string and adapted for placement on said string approximately one-fourth of the distance from said lower stabilizer to said second stabilizer, each of said stabilizers comprising a generally cylindrical member having an axial bore therethrough, a plurality of fluid channels in the surface of said member and extending longitudinally thereof, lands extending circumferentially between said fluid channels, the outside diameter of said lands being substantially equal to the nominal diameter of the well bore, and the depth of said fluid channels being between 0.140 to 0.221 times the outside diameter of the said lands.

References Cited UNITED STATES PATENTS 2,079,449 5/1937 Haldeman -325 X 2,352,412 6/1944 Sandstone 166-241 2,388,416 11/1945 Johnson 166-241 2,794,617 6/1957 Yancey 175-325 X 2,829,864 4/1958 Knapp 175325 2,877,062 3/1-959 Hall 308-4 2,973,996 3/1961 Self 175-323 X 3,306,378 2/1967 Williams 175-325 3,338,069 8/1967 Ortloif 175-320 X NILE C. BYERS, 111., Primary Examiner.

U.S. Cl.X.R. 308-4 

